In recent years, the development of the information technology sector has meant that people's day-to-day use of the Internet has continually increased; and the convenience of Internet services has increased in kind. Unfortunately, abusive users such as hackers can exploit these Internet resources for their own purpose by using simulated users or automated bots (also referred to as Internet bots, computer bots, or web robots) that can reduce the performance of online systems for legitimate users.
In order to avoid this situation, it is important to be able to distinguish between valid human users and invalid computer bots on the Internet. Web based content portals and sites requiring any sort of authentication have used the ‘CAPTCHA’ as a mechanism to differentiate between humans and bots. The test is designed so that human users can answer the questions or challenges easily, but computer-program based imitators face considerably greater challenge in answering the questions using optical readers. By considering the quality or correctness of a response, a judging computer can determine whether the tested user is a human or a computer bot.
In recent years a lot of progress has been made to make the CAPTCHAs harder for bots and yet easier for humans to solve. However there is an inherent flaw with traditional CAPTCHAs. A CAPTCHA that is hard for a bot to crack is also hard for a human to solve. Dial-up the difficulty and both bots and humans fail. Dial down the complexity and the abuse and farmed accounts go up. Difficult CAPTCHAs ultimately lead to user frustration and eventual drop-off from registration forms and other services.